The chief focus of this project has been on the systematic examination of the relationship between psychosocial stress, induced by alterations in the physical and/or social environment, and concomitant changes in adrenal activation and immune measures, as well on the possible social modulation of stress. The overall objective of these studies is to improve our understanding of the role of psychosocial variables in either inducing or modulating physiological responses which may have either a positive or an adverse impact on health. In order to examine the relationship among individual reactivity, social support and response to psychosocial stress, juvenile rhesus monkeys were studied in the context of the natal social group. Following assessment of reactivity, as measured by cortisol response to a separation, and social support, measured by behavioral patterns, subjects were rank ordered on each of these measures then divided into two groups (control and experimental) ma tched for reactivity, support, gender and social rank. The experimental subjects were studied in the presence of a stress stimulus cortisol levels, descriptive immune measures and the response to immunization with KLH and tetanus toxoid, non-replicating antigens allowing for independent assessment of response, were measured. Controls were assessed in an identical sequence absent the stress stimulus. Results revealed a significant effect of both reactivity and social support in influencing hormonal and immune response. This work was framed by the emergent clinical evidence demonstrating a link between psychosocial stress and both the incidence and course of diverse illnesses, and has now provided parallel documentation in the laboratory of the interplay among behavioral, endocrine and immunological variables.